Description

The /usr/xpg4/bin/sh utility is a standards compliant shell. This utility provides all
the functionality of /usr/bin/ksh, except in cases where differences in behavior exist.
See Arithmetic Expansions section for details.

/usr/bin/ksh is a command and programming language that executes commands read from
a terminal or a file. rksh is a restricted version of the
command interpreter ksh; it is used to set up login names and
execution environments whose capabilities are more controlled than those of the standard shell.
See the Invocation section for the meaning of arguments to the shell.

Definitions

A metacharacter is one of the following characters:

; & ( ) | < >NEWLINE SPACE TAB

A blank is a TAB or a SPACE. An identifier is a
sequence of letters, digits, or underscores starting with a letter or underscore.
Identifiers are used as names for functions and variables. A word is
a sequence of characters separated by one or more non-quoted metacharacters.

A command is a sequence of characters in the syntax of the
shell language. The shell reads each command and carries out the desired
action either directly or by invoking separate utilities. A special-command is a
command that is carried out by the shell without creating a separate process.
Except for documented side effects, most special commands can be implemented as
separate utilities.

Commands

A simple-command is a sequence of blank-separated words which can be preceded
by a variable assignment list. See Environment. The first word specifies the
name of the command to be executed. Except as specified, the remaining
words are passed as arguments to the invoked command. The command name is
passed as argument 0 (see exec(2)). The value of a simple-command is
its exit status if it terminates normally. If it terminates abnormally due to
receipt of a signal, the value is the signal number plus 128.
See signal.h(3HEAD) for a list of signal values. Obviously, normal exit status
values 129 to 255 cannot be distinguished from abnormal exit caused by
receiving signal numbers 1 to 127.

A pipeline is a sequence of one or more commands separated by
|. The standard output of each command but the last is connected
by a pipe(2) to the standard input of the next command. Each
command is run as a separate process; the shell waits for the
last command to terminate. The exit status of a pipeline is the
exit status of the last command.

A list is a sequence of one or more pipelines separated by
;, &, &&, or | |, and optionally terminated by ;, &, or |&.
Of these five symbols, ;, &, and |& have equal precedence, which
is lower than that of && and | |. The symbols && and
| | also have equal precedence. A semicolon (;) causes sequential execution of
the preceding pipeline; an ampersand (&) causes asynchronous execution of the preceding
pipeline (that is, the shell does not wait for that pipeline to finish).
The symbol |& causes asynchronous execution of the preceding command or pipeline
with a two-way pipe established to the parent shell.

The standard input and output of the spawned command can be written
to and read from by the parent shell using the -p option
of the special commands read and print described in Special Commands. The symbol
&& ( | |) causes the list following it to be executed only if
the preceding pipeline returns 0 (or a non-zero) value. An arbitrary number
of new-lines can appear in a list, instead of a semicolon, to delimit
a command.

A command is either a simple-command or one of the following. Unless
otherwise stated, the value returned by a command is that of the
last simple-command executed in the command.

foridentifier [ inword ... ] ; dolist; done

Each time a for command is executed, identifier is set to the next word taken from the inword list. If inword ... is omitted, then the for command executes the dolist once for each positional parameter that is set. See Parameter Substitution. Execution ends when there are no more words in the list.

selectidentifier [ inword ... ] ; dolist; done

A select command prints to standard error (file descriptor 2), the set of words, each preceded by a number. If inword ... is omitted, then the positional parameters are used instead. See Parameter Substitution. The PS3 prompt is printed and a line is read from the standard input. If this line consists of the number of one of the listed words, then the value of the variable identifier is set to the word corresponding to this number. If this line is empty the selection list is printed again. Otherwise the value of the variable identifier is set to NULL. (See Blank Interpretation about NULL). The contents of the line read from standard input is saved in the shell variable REPLY. The list is executed for each selection until a break or EOF is encountered. If the REPLY variable is set to NULL by the execution of list, then the selection list is printed before displaying the PS3 prompt for the next selection.

casewordin [ pattern [ | pattern ] )list;; ] ... esac

A case command executes the list associated with the first pattern that matches word. The form of the patterns is the same as that used for file-name generation. See File Name Generation.

iflist; thenlist; [ eliflist; thenlist; ... ] [ elselist; ] fi

The list following if is executed and, if it returns an exit status of 0, the list following the first then is executed. Otherwise, the list following elif is executed and, if its value is 0, the list following the next then is executed. Failing that, the elselist is executed. If no elselist or thenlist is executed, then the if command returns 0 exit status.

whilelist; dolist; done

untillist; dolist; done

A while command repeatedly executes the whilelist and, if the exit status of the last command in the list is 0, executes the dolist; otherwise the loop terminates. If no commands in the dolist are executed, then the while command returns 0 exit status. until can be used in place of while to negate the loop termination test.

(list)

Execute list in a separate environment. If two adjacent open parentheses are needed for nesting, a space must be inserted to avoid arithmetic evaluation.

{list}

list is simply executed. Unlike the metacharacters ( and ), { and } are reserved words and must occur at the beginning of a line or after a ; in order to be recognized.

[[expression]]

Evaluates expression and returns 0 exit status when expression is true. See Conditional Expressions for a description of expression.

functionidentifier{list;}

identifier( ) {list;}

Define a function which is referenced by identifier. The body of the function is the list of commands between { and }. See Functions.

timepipeline

The pipeline is executed and the elapsed time as well as the user and system time are printed to standard error.

The following reserved words are only recognized as the first word of
a command and when not quoted:

! if then else elif fi case
esac for while until do done { }
function select time [[ ]]

Comments

A word beginning with # causes that word and all the following
characters up to a new-line to be ignored.

Aliasing

The first word of each command is replaced by the text of
an alias if an alias for this word has been defined. An
alias name consists of any number of characters excluding metacharacters, quoting characters,
file expansion characters, parameter and command substitution characters, and =. The replacement
string can contain any valid shell script including the metacharacters listed above.
The first word of each command in the replaced text, other than
any that are in the process of being replaced, is tested for
aliases. If the last character of the alias value is a blank
then the word following the alias is also be checked for alias
substitution. Aliases can be used to redefine special builtin commands but cannot
be used to redefine the reserved words listed above. Aliases can be
created, listed, and exported with the alias command and can be removed with
the unalias command. Exported aliases remain in effect for scripts invoked by
name, but must be reinitialized for separate invocations of the shell. See
Invocation. To prevent infinite loops in recursive aliasing, if the shell is
not currently processing an alias of the same name, the word is replaced
by the value of the alias; otherwise, it is not be replaced.

Aliasing is performed when scripts are read, not while they are executed.
Therefore, for an alias to take effect, the alias definition command has
to be executed before the command which references the alias is read.

Aliases are frequently used as a short hand for full path names.
An option to the aliasing facility allows the value of the alias
to be automatically set to the full pathname of the corresponding command.
These aliases are called tracked aliases. The value of a tracked alias
is defined the first time the corresponding command is looked up and
becomes undefined each time the PATH variable is reset. These aliases remain
tracked so that the next subsequent reference redefines the value. Several tracked aliases
are compiled into the shell. The -h option of the set command
makes each referenced command name into a tracked alias.

The following exported aliases are compiled into (and built-in to) the shell but
can be unset or redefined:

is a never-ending sequence of Hello, World strings to the screen. However, if
the user types:

$ foo while

the result is an ls listing of /. Since the alias substitution
for foo ends in a space character, the next word is checked
for alias substitution. The next word, while, has also been aliased, so
it is substituted as well. Since it is not in the proper position
as a command word, it is not recognized as a reserved word.

If the user types:

$ foo; while

while retains its normal reserved-word properties.

Tilde Substitution

After alias substitution is performed, each word is checked to see if
it begins with an unquoted ~. If it does, then the word
up to a / is checked to see if it matches a
user name. If a match is found, the ~ and the matched
login name are replaced by the login directory of the matched user. This
is called a tilde substitution. If no match is found, the original
text is left unchanged. A ~ by itself, or in front of
a /, is replaced by $HOME. A ~ followed by a + or
- is replaced by $PWD and $OLDPWD, respectively.

In addition, tilde substitution is attempted when the value of a variable assignment
begins with a ~.

Tilde Expansion

A tilde-prefix consists of an unquoted tilde character at the beginning of
a word, followed by all of the characters preceding the first unquoted
slash in the word, or all the characters in the word if
there is no slash. In an assignment, multiple tilde-prefixes can be used: at
the beginning of the word (that is, following the equal sign of
the assignment), following any unquoted colon or both. A tilde-prefix in an
assignment is terminated by the first unquoted colon or slash. If none
of the characters in the tilde-prefix are quoted, the characters in the tilde-prefix
following the tilde are treated as a possible login name from the
user database.

A portable login name cannot contain characters outside the set given in
the description of the LOGNAME environment variable. If the login name is
null (that is, the tilde-prefix contains only the tilde), the tilde-prefix is
replaced by the value of the variable HOME. If HOME is unset, the
results are unspecified. Otherwise, the tilde-prefix is replaced by a pathname of
the home directory associated with the login name obtained using the getpwnam
function. If the system does not recognize the login name, the results
are undefined.

Tilde expansion generally occurs only at the beginning of words, but an
exception based on historical practice has been included:

PATH=/posix/bin:~dgk/bin

is eligible for tilde expansion because tilde follows a colon and none
of the relevant characters is quoted. Consideration was given to prohibiting this
behavior because any of the following are reasonable substitutes:

With the first command, explicit colons are used for each directory. In
all cases, the shell performs tilde expansion on each directory because all
are separate words to the shell.

Expressions in operands such as:

make -k mumble LIBDIR=~chet/lib

do not qualify as shell variable assignments and tilde expansion is not
performed (unless the command does so itself, which make does not).

The special sequence $~ has been designated for future implementations to evaluate
as a means of forcing tilde expansion in any word.

Because of the requirement that the word not be quoted, the following
are not equivalent; only the last causes tilde expansion:

\~hlj/ ~h\lj/ ~"hlj"/ ~hlj\/ ~hlj/

The results of giving tilde with an unknown login name are undefined
because the KornShell ~+ and ~- constructs make use of this condition,
but, in general it is an error to give an incorrect login
name with tilde. The results of having HOME unset are unspecified because some
historical shells treat this as an error.

Command Substitution

The standard output from a command enclosed in parenthesis preceded by a
dollar sign (that is, $(command)) or a pair of grave accents (``)
can be used as part or all of a word. Trailing new-lines are
removed. In the second (archaic) form, the string between the quotes is
processed for special quoting characters before the command is executed. See Quoting.
The command substitution $(catfile) can be replaced by the equivalent but faster
$(<file). Command substitution of most special commands that do not perform input/output
redirection are carried out without creating a separate process.

Command substitution allows the output of a command to be substituted in
place of the command name itself. Command substitution occurs when the command
is enclosed as follows:

$(command)

or (backquoted version):

`command`

The shell expands the command substitution by executing command in a subshell
environment and replacing the command substitution (the text of command plus the
enclosing $() or backquotes) with the standard output of the command, removing sequences
of one or more newline characters at the end of the substitution.
Embedded newline characters before the end of the output is not be
removed; however, they can be treated as field delimiters and eliminated during
field splitting, depending on the value of IFS and quoting that is in
effect.

Within the backquoted style of command substitution, backslash shall retain its literal
meaning, except when followed by:

$ ` \

(dollar-sign, backquote, backslash). The search for the matching backquote is satisfied by
the first backquote found without a preceding backslash. During this search, if
a non-escaped backquote is encountered within a shell comment, a here-document, an
embedded command substitution of the $(command) form, or a quoted string, undefined results
occur. A single- or double-quoted string that begins, but does not end,
within the `...` sequence produces undefined results.

With the $(command) form, all characters following the open parenthesis to the
matching closing parenthesis constitute the command. Any valid shell script can be
used for command, except:

The results of command substitution are not field splitting and pathname expansion
processed for further tilde expansion, parameter expansion, command substitution or arithmetic expansion.
If a command substitution occurs inside double-quotes, it is not be performed
on the results of the substitution.

Command substitution can be nested. To specify nesting within the backquoted version,
the application must precede the inner backquotes with backslashes; for example:

`\`command\``

The $() form of command substitution solves a problem of inconsistent behavior
when using backquotes. For example:

Command

Output

echo '\$x'

\$x

echo `echo '\$x'`

$x

echo $(echo '\$x')

\$x

Additionally, the backquoted syntax has historical restrictions on the contents of the
embedded command. While the new $() form can process any kind of
valid embedded script, the backquoted form cannot handle some valid scripts that
include backquotes. For example, these otherwise valid embedded scripts do not work in
the left column, but do work on the right:

echo `

echo $(

cat <<eeof

cat
<<eeof

a here-doc with `

a here-doc with )

eof

eof

`

)

echo `

echo $(

echo abc # a
comment with `

echo abc # a comment with )

`

)

echo `

echo $(

echo '`'

echo
')'

`

)

Because of these inconsistent behaviors, the backquoted variety of command substitution is
not recommended for new applications that nest command substitutions or attempt to
embed complex scripts.

If the command substitution consists of a single subshell, such as:

$( (command) )

a portable application must separate the $( and ( into two tokens
(that is, separate them with white space). This is required to avoid
any ambiguities with arithmetic expansion.

Arithmetic Expansion

An arithmetic expression enclosed in double parentheses preceded by a dollar sign
( $((arithmetic-expression)) ) is replaced by the value of the arithmetic expression
within the double parenthesis. Arithmetic expansion provides a mechanism for evaluating an arithmetic
expression and substituting its value. The format for arithmetic expansion is as
follows:

$((expression))

The expression is treated as if it were in double-quotes, except that
a double-quote inside the expression is not treated specially. The shell expands
all tokens in the expression for parameter expansion, command substitution and quote
removal.

Next, the shell treats this as an arithmetic expression and substitute the
value of the expression. The arithmetic expression is processed according to the
rules of the ISO C with the following exceptions:

Only integer arithmetic is required.

The sizeof() operator and the prefix and postfix ++ and - - operators are not required.

Selection, iteration, and jump statements are not supported.

/usr/bin/ksh and /usr/bin/rksh treat prefix 0 through 9 as decimal constants. See the following examples:

Command

Result in /bin/ksh

Result in /usr/xpg4/bin/sh

echo $((010+10))

20

18

echo $((019+10))

29

error

[ 10 —le $((011)) ]

true

false

As an extension, the shell can recognize arithmetic expressions beyond those listed.
If the expression is invalid, the expansion fails and the shell writes
a message to standard error indicating the failure.

Process Substitution

This feature is available in SunOS and only on versions of the
UNIX operating system that support the /dev/fd directory for naming open files.
Each command argument of the form <(list) or >(list) runs process list
asynchronously connected to some file in /dev/fd. The name of this file
becomes the argument to the command. If the form with > is
selected, then writing on this file provides input for list. If < is
used, then the file passed as an argument contains the output of
the list process. For example:

paste <(cut -f1 file1) <(cut -f3 file2) | tee >(process1) >(process2)

cuts fields 1 and 3 from the files file1 and file2, respectively,
pastes the results together, and sends it to the processes process1 and
process2, as well as putting it onto the standard output. The file, which
is passed as an argument to the command, is a UNIX pipe(2)
so programs that expect to lseek(2) on the file does not work.

Parameter Substitution

A parameter is an identifier, one or more digits, or any of
the characters *, @, #, ?, -, $, and !. A variable (a
parameter denoted by an identifier) has a value and zero or more
attributes. variables can be assigned values and attributes by using the typeset special
command. The attributes supported by the shell are described later with the
typeset special command. Exported variables pass values and attributes to the environment.

The shell supports a one-dimensional array facility. An element of an array
variable is referenced by a subscript. A subscript is denoted by a
[, followed by an arithmetic expression, followed by a ]. See Arithmetic Evaluation. To assign
values to an array, use set-Aname value.... The value of
all subscripts must be in the range of 0 through 4095. Arrays need
not be declared. Any reference to a variable with a valid subscript
is legal and an array is created if necessary. Referencing an array
without a subscript is equivalent to referencing the element 0. If an
array identifier with subscript * or @ is used, then the value
for each of the elements is substituted (separated by a field separator
character).

The value of a variable can be assigned by writing:

name=value [ name=value ] ...

If the integer attribute, -i, is set for name, the value is
subject to arithmetic evaluation.

Positional parameters, parameters denoted by a number, can be assigned values with
the set special command. Parameter $0 is set from argument zero when
the shell is invoked. If parameter is one or more digits then
it is a positional parameter. A positional parameter of more than one digit
must be enclosed in braces.

Parameter Expansion

The format for parameter expansion is as follows:

${expression}

where expression consists of all characters until the matching }. Any }
escaped by a backslash or within a quoted string, and characters in
embedded arithmetic expansions, command substitutions and variable expansions, are not examined in determining
the matching }.

The simplest form for parameter expansion is:

${parameter}

The value, if any, of parameter is substituted.

The parameter name or symbol can be enclosed in braces, which are
optional except for positional parameters with more than one digit or when
parameter is followed by a character that could be interpreted as part
of the name. The matching closing brace are determined by counting brace levels,
skipping over enclosed quoted strings and command substitutions.

If the parameter name or symbol is not enclosed in braces, the
expansion uses the longest valid name whether or not the symbol represented
by that name exists. When the shell is scanning its input to
determine the boundaries of a name, it is not bound by its
knowledge of what names are already defined. For example, if F is a
defined shell variable, the command:

echo $Fred

does not echo the value of $F followed by red; it selects
the longest possible valid name, Fred, which in this case might be
unset.

If a parameter expansion occurs inside double-quotes:

Pathname expansion is not be performed on the results of the expansion.

Field splitting is not performed on the results of the expansion, with the exception of @.

In addition, a parameter expansion can be modified by using one of
the following formats. In each case that a value of word is
needed (based on the state of parameter), word is subjected to tilde
expansion, parameter expansion, command substitution and arithmetic expansion. If word is not needed,
it is not expanded. The } character that delimits the following parameter
expansion modifications is determined as described previously in this section and in
dquote. (For example, ${foo-bar}xyz} would result in the expansion of foo followed
by the string xyz} if foo is set, else the string barxyz}).

${parameter:-word}

Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.

${parameter:=word}

Assign Default Values. If parameter is unset or null, the expansion of word is assigned to parameter. In all cases, the final value of parameter is substituted. Only variables, not positional parameters or special parameters, can be assigned in this way.

${parameter:?[word]}

Indicate Error if Null or Unset. If parameter is unset or null, the expansion of word (or a message indicating it is unset if word is omitted) is written to standard error and the shell exits with a non-zero exit status. Otherwise, the value of parameter is substituted. An interactive shell need not exit.

${parameter:+[word]}

Use Alternative Value. If parameter is unset or null, null is substituted. Otherwise, the expansion of word is substituted.

In the parameter expansions shown previously, use of the colon in the
format results in a test for a parameter that is unset or
null. Omission of the colon results in a test for a parameter
that is only unset. The following two tables summarize the effect of
the colon:

parameter set and not null

parameter set and null

${parameter:-word}

substitute parameter

substitute word

${parameter-word}

substitute parameter

substitute
null

${parameter:=word}

substitute parameter

assign word

${parameter=word}

substitute parameter

substitute parameter

${parameter:?word}

substitute parameter

error, exit

${parameter?word}

substitute parameter

substitute null

${parameter:+word}

substitute word

substitute null

${parameter+word}

substitute word

substitute
word

parameter unset

${parameter:-word}

substitute word

${parameter-word}

substitute word

${parameter:=word}

assign word

${parameter=word}

assign null

${parameter:?word}

error, exit

${parameter?word}

error,exit

${parameter:+word}

substitute null

${parameter+word}

substitute null

In all cases shown with “substitute”, the expression is replaced with the
value shown. In all cases shown with “assign”, parameter is assigned that
value, which also replaces the expression.

${#parameter}

String Length. The length in characters of the value of parameter. If parameter is * or @, then all the positional parameters, starting with $1, are substituted (separated by a field separator character).

The following four varieties of parameter expansion provide for substring processing. In
each case, pattern matching notation (see patmat), rather than regular expression notation,
is used to evaluate the patterns. If parameter is * or @,
then all the positional parameters, starting with $1, are substituted (separated by
a field separator character). Enclosing the full parameter expansion string in double-quotes
does not cause the following four varieties of pattern characters to be
quoted, whereas quoting characters within the braces has this effect.

${parameter%word}

Remove Smallest Suffix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the smallest portion of the suffix matched by the pattern deleted.

${parameter%%word}

Remove Largest Suffix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the largest portion of the suffix matched by the pattern deleted.

${parameter#word}

Remove Smallest Prefix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the smallest portion of the prefix matched by the pattern deleted.

${parameter##word}

Remove Largest Prefix Pattern. The word is expanded to produce a pattern. The parameter expansion then results in parameter, with the largest portion of the prefix matched by the pattern deleted.

Examples:

${parameter:-word}

In this example, ls is executed only if x is null or
unset. (The $(ls) command substitution notation is explained in Command Substitution above.)

${x:-$(ls)}

${parameter:=word}

unset X
echo ${X:=abc}
abc

${parameter:?word}

unset posix
echo ${posix:?}
sh: posix: parameter null or not set

${parameter:+word}

set a b c
echo ${3:+posix}
posix

${#parameter}

HOME=/usr/posix
echo ${#HOME}
10

${parameter%word}

x=file.c
echo ${x%.c}.o
file.o

${parameter%%word}

x=posix/src/std
echo ${x%%/*}
posix

${parameter#word}

x=$HOME/src/cmd
echo ${x#$HOME}
/src/cmd

${parameter##word}

x=/one/two/three
echo ${x##*/}
three

Parameters Set by Shell

The following parameters are automatically set by the shell:

#

The number of positional parameters in decimal.

-

Flags supplied to the shell on invocation or by the set command.

?

The decimal value returned by the last executed command.

$

The process number of this shell.

_

Initially, the value of _ is an absolute pathname of the shell or script being executed as passed in the environment. Subsequently it is assigned the last argument of the previous command. This parameter is not set for commands which are asynchronous. This parameter is also used to hold the name of the matching MAIL file when checking for mail.

!

The process number of the last background command invoked.

ERRNO

The value of errno as set by the most recently failed system call. This value is system dependent and is intended for debugging purposes.

LINENO

The line number of the current line within the script or function being executed.

OLDPWD

The previous working directory set by the cd command.

OPTARG

The value of the last option argument processed by the getopts special command.

OPTIND

The index of the last option argument processed by the getopts special command.

PPID

The process number of the parent of the shell.

PWD

The present working directory set by the cd command.

RANDOM

Each time this variable is referenced, a random integer, uniformly distributed between 0 and 32767, is generated. The sequence of random numbers can be initialized by assigning a numeric value to RANDOM.

REPLY

This variable is set by the select statement and by the read special command when no arguments are supplied.

SECONDS

Each time this variable is referenced, the number of seconds since shell invocation is returned. If this variable is assigned a value, then the value returned upon reference is the value that was assigned plus the number of seconds since the assignment.

Variables Used by Shell

The following variables are used by the shell:

CDPATH

The search path for the cd command.

COLUMNS

If this variable is set, the value is used to define the width of the edit window for the shell edit modes and for printing select lists.

EDITOR

If the value of this variable ends in emacs, gmacs, or vi and the VISUAL variable is not set, then the corresponding option is turned on. See the set special command.

ENV

This variable, when and only when an interactive shell is invoked, is subjected to parameter expansion by the shell and the resulting value is used as a pathname of a file containing shell commands to execute in the current environment. The file need not be executable. If the expanded value of ENV is not an absolute pathname, the results are unspecified. ENV is ignored if the user's real and effective user IDs or real and effective group IDs are different.

This variable can be used to set aliases and other items local to the invocation of a shell. The file referred to by ENV differs from $HOME/.profile in that .profile is typically executed at session startup, whereas the ENV file is executed at the beginning of each shell invocation. The ENV value is interpreted in a manner similar to a dot script, in that the commands are executed in the current environment and the file needs to be readable, but not executable. However, unlike dot scripts, no PATH searching is performed. This is used as a guard against Trojan Horse security breaches.

FCEDIT

The default editor name for the fc command.

FPATH

The search path for function definitions. By default, the FPATH directories are searched after the PATH variable. If an executable file is found, then it is read and executed in the current environment. FPATH is searched before PATH when a function with the -u attribute is referenced. The preset alias autoload causes a function with the -u attribute to be created.

HISTFILE

If this variable is set when the shell is invoked, then the value is the pathname of the file that is used to store the command history. See Command re-entry.

HISTSIZE

If this variable is set when the shell is invoked, then the number of previously entered commands that are accessible by this shell is greater than or equal to this number. The default is 128.

HOME

The default argument (home directory) for the cd command.

IFS

Internal field separators, normally space, tab, and new-line that are used to separate command words which result from command or parameter substitution and for separating words with the special command read. The first character of the IFS variable is used to separate arguments for the $* substitution. See Quoting.

LANG

Provide a default value for the internationalization variables that are unset or null. If any of the internationalization variables contains an invalid setting, the utility behaves as if none of the variables had been defined.

LC_ALL

This variable provides a default value for the LC_* variables.

LC_COLLATE

This variable determines the behavior of range expressions, equivalence classes and multi-byte character collating elements within pattern matching.

LC_CTYPE

Determines how the shell handles characters. When LC_CTYPE is set to a valid value, the shell can display and handle text and filenames containing valid characters for that locale. If LC_CTYPE (see environ(5)) is not set in the environment, the operational behavior of the shell is determined by the value of the LANG environment variable. If LC_ALL is set, its contents are used to override both the LANG and the other LC_* variables.

LC_MESSAGES

This variable determines the language in which messages should be written.

LINENO

This variable is set by the shell to a decimal number representing the current sequential line number (numbered starting with 1) within a script or function before it executes each command. If the user unsets or resets LINENO, the variable can lose its special meaning for the life of the shell. If the shell is not currently executing a script or function, the value of LINENO is unspecified.

LINES

If this variable is set, the value is used to determine the column length for printing select lists. Select lists print vertically until about two-thirds of LINES lines are filled.

MAIL

If this variable is set to the name of a mail file and the MAILPATH variable is not set, then the shell informs the user of arrival of mail in the specified file.

MAILCHECK

This variable specifies how often (in seconds) the shell checks for changes in the modification time of any of the files specified by the MAILPATH or MAIL variables. The default value is 600 seconds. When the time has elapsed the shell checks before issuing the next prompt.

MAILPATH

A colon (:) separated list of file names. If this variable is set, then the shell informs the user of any modifications to the specified files that have occurred within the last MAILCHECK seconds. Each file name can be followed by a ? and a message that is printed. The message undergoes parameter substitution with the variable $_ defined as the name of the file that has changed. The default message is you have mail in $_.

NLSPATH

Determine the location of message catalogues for the processing of LC_MESSAGES.

PATH

The search path for commands. See Execution. The user cannot change PATH if executing under rksh (except in .profile).

PPID

This variable is set by the shell to the decimal process ID of the process that invoked the shell. In a subshell, PPID is set to the same value as that of the parent of the current shell. For example, echo $PPID and (echo $PPID) would produce the same value.

PS1

The value of this variable is expanded for parameter substitution to define the primary prompt string which by default is ``$ ''. The character ! in the primary prompt string is replaced by the command number. See Command Re-entry. Two successive occurrences of ! produces a single ! when the prompt string is printed.

PS2

Secondary prompt string, by default ``> ''.

PS3

Selection prompt string used within a select loop, by default ``#? ''.

PS4

The value of this variable is expanded for parameter substitution and precedes each line of an execution trace. If omitted, the execution trace prompt is ``+ ''.

PWD

Set by the shell to be an absolute pathname of the current working directory, containing no components of type symbolic link, no components that are dot, and no components that are dot-dot when the shell is initialized. If an application sets or unsets the value of PWD, the behaviors of the cd and pwd utilities are unspecified

SHELL

The pathname of the shell is kept in the environment. At invocation, if the basename of this variable is rsh, rksh, or krsh, then the shell becomes restricted.

TMOUT

If set to a value greater than zero, the shell terminates if a command is not entered within the prescribed number of seconds after issuing the PS1 prompt. The shell can be compiled with a maximum bound for this value which cannot be exceeded.

VISUAL

If the value of this variable ends in emacs, gmacs, or vi, then the corresponding option is turned on. See Special Command set.

The shell gives default values to PATH, PS1, PS2, PS3, PS4, MAILCHECK,
FCEDIT, TMOUT, and IFS, while HOME, SHELL, ENV, and MAIL are not set
at all by the shell (although HOMEis set by login(1)). On
some systems MAIL and SHELL are also set by login.

Blank Interpretation

After parameter and command substitution, the results of substitutions are scanned for
the field separator characters (those found in IFS) and split into distinct
arguments where such characters are found. Explicit null arguments ( "" )
or ('') are retained. Implicit null arguments (those resulting from parameters that have
no values) are removed.

File Name Generation

Following substitution, each command word is scanned for the characters *, ?,
and [ unless the -f option has been set. If one of
these characters appears, the word is regarded as a pattern. The word is
replaced with lexicographically sorted file names that match the pattern. If no
file name is found that matches the pattern, the word is left
unchanged. When a pattern is used for file name generation, the character period
(.) at the start of a file name or immediately following a
/, as well as the character / itself, must be matched explicitly.
A file name beginning with a period is not matched with a
pattern with the period inside parentheses. That is, ls .@(r*) would locate a file
named .restore, but ls @(.r*) would not. In other instances of pattern matching,
the / and . are not treated specially.

*

Matches any string, including the null string.

?

Matches any single character.

[...]

Matches any one of the enclosed characters. A pair of characters separated by - matches any character lexically between the pair, inclusive. If the first character following the opening “[” is a “! ”, then any character not enclosed is matched. A - can be included in the character set by putting it as the first or last character.

A pattern-list is a list of one or more patterns separated from
each other with a |. Composite patterns can be formed with one
or more of the following:

?(pattern-list)

Optionally matches any one of the given patterns.

*(pattern-list)

Matches zero or more occurrences of the given patterns.

+(pattern-list)

Matches one or more occurrences of the given patterns.

@(pattern-list)

Matches exactly one of the given patterns.

!(pattern-list)

Matches anything, except one of the given patterns.

Quoting

Each of the metacharacters listed above (see Definitions) has a special meaning
to the shell and causes termination of a word unless quoted. A
character can be quoted (that is, made to stand for itself) by
preceding it with a \ . The pair \ NEWLINE is removed. All characters enclosed
between a pair of single quote marks (' ') are quoted. A single
quote cannot appear within single quotes. Inside double quote marks (""), parameter and
command substitution occur and \ quotes the characters \ , `, ", and
$. The meaning of $* and $@ is identical when not quoted
or when used as a parameter assignment value or as a file name.
However, when used as a command argument, $* is equivalent to ``$1d $2d...'',
where d is the first character of the IFS variable, whereas $@ is
equivalent to $1$2 . . .. Inside grave quote marks (``), \ quotes
the characters \, ', and $. If the grave quotes occur within
double quotes, then \ also quotes the character ".

The special meaning of reserved words or aliases can be removed by
quoting any character of the reserved word. The recognition of function names
or special command names listed cannot be altered by quoting them.

Arithmetic Evaluation

An ability to perform integer arithmetic is provided with the special command
let. Evaluations are performed using long arithmetic. Constants are of the form
[ base# ] n where base is a decimal number between two
and thirty-six representing the arithmetic base and n is a number in
that base. If base is omitted then base 10 is used.

An arithmetic expression uses the same syntax, precedence, and associativity of expression
as the C language. All the integral operators, other than ++, –;,
?:, and , are supported. Variables can be referenced by name within an
arithmetic expression without using the parameter substitution syntax. When a variable is
referenced, its value is evaluated as an arithmetic expression.

An internal integer representation of a variable can be specified with the
-i option of the typeset special command. Arithmetic evaluation is performed on
the value of each assignment to a variable with the -i attribute. If
you do not specify an arithmetic base, the first assignment to the
variable determines the arithmetic base. This base is used when parameter substitution
occurs.

Since many of the arithmetic operators require quoting, an alternative form of
the let command is provided. For any command which begins with a
((, all the characters until a matching )) are treated as a
quoted expression. More precisely, ((. . .)) is equivalent to let" . . .".

Prompting

When used interactively, the shell prompts with the parameter expanded value of
PS1 before reading a command. If at any time a new-line is
typed and further input is needed to complete a command, then the
secondary prompt (that is, the value of PS2) is issued.

Conditional Expressions

A conditional expression is used with the [[ compound command to test attributes
of files and to compare strings. Word splitting and file name generation
are not performed on the words between [[ and ]]. Each expression can
be constructed from one or more of the following unary or binary
expressions:

-afile

True, if file exists.

-bfile

True, if file exists and is a block special file.

-cfile

True, if file exists and is a character special file.

-dfile

True, if file exists and is a directory.

-efile

True, if file exists.

-ffile

True, if file exists and is an ordinary file.

-gfile

True, if file exists and has its setgid bit set.

-hfile

True, if file exists and is a symbolic link.

-kfile

True, if file exists and has its sticky bit set.

-nstring

True, if length of string is non-zero.

-ooption

True, if option named option is on.

-pfile

True, if file exists and is a fifo special file or a pipe.

-rfile

True, if file exists and is readable by current process.

-sfile

True, if file exists and has size greater than zero.

-tfildes

True, if file descriptor number fildes is open and associated with a terminal device.

-ufile

True, if file exists and has its setuid bit set.

-wfile

True, if file exists and is writable by current process.

-xfile

True, if file exists and is executable by current process. If file exists and is a directory, then the current process has permission to search in the directory.

-zstring

True, if length of string is zero.

-Lfile

True, if file exists and is a symbolic link.

-Ofile

True, if file exists and is owned by the effective user id of this process.

-Gfile

True, if file exists and its group matches the effective group id of this process.

-Sfile

True, if file exists and is a socket.

file1-ntfile2

True, if file1 exists and is newer than file2.

file1-otfile2

True, if file1 exists and is older than file2.

file1-effile2

True, if file1 and file2 exist and refer to the same file.

string

True if the string string is not the null string.

string=pattern

True, if string matches pattern.

string!=pattern

True, if string does not match pattern.

string1<string2

True, if string1 comes before string2 based on strings interpreted as appropriate to the locale setting for category LC_COLLATE.

string1>string2

True, if string1 comes after string2 based on strings interpreted as appropriate to the locale setting for category LC_COLLATE.

exp1-eqexp2

True, if exp1 is equal to exp2.

exp1-neexp2

True, if exp1 is not equal to exp2.

exp1-ltexp2

True, if exp1 is less than exp2.

exp1-gtexp2

True, if exp1 is greater than exp2.

exp1-leexp2

True, if exp1 is less than or equal to exp2.

exp1-geexp2

True, if exp1 is greater than or equal to exp2.

In each of the above expressions, if file is of the form
/dev/fd/n, where n is an integer, then the test is applied to
the open file whose descriptor number is n.

A compound expression can be constructed from these primitives by using any
of the following, listed in decreasing order of precedence.

(expression)

True, if expression is true. Used to group expressions.

!expression

True if expression is false.

expression1&&expression2

True, if expression1 and expression2 are both true.

expression1||expression2

True, if either expression1 or expression2 is true.

Input/Output

Before a command is executed, its input and output can be redirected
using a special notation interpreted by the shell. The following can appear
anywhere in a simple-command or can precede or follow a command and
are not passed on to the invoked command. Command and parameter substitution occur
before word or digit is used except as noted. File name generation
occurs only if the pattern matches a single file, and blank interpretation
is not performed.

<word

Use file word as standard input (file descriptor 0).

>word

Use file word as standard output (file descriptor 1). If the file does not exist then it is created. If the file exists, and the noclobber option is on, this causes an error; otherwise, it is truncated to zero length.

>|word

Sames as >, except that it overrides the noclobber option.

>>word

Use file word as standard output. If the file exists, output is appended to it (by first seeking to the EOF). Otherwise, the file is created.

<>word

Open file word for reading and writing as standard input.

<< [-]word

The shell input is read up to a line that is the same as word, or to an EOF. No parameter substitution, command substitution, or file name generation is performed on word. The resulting document, called a here-document, becomes the standard input. If any character of word is quoted, no interpretation is placed upon the characters of the document. Otherwise, parameter and command substitution occur, \NEWLINE is ignored, and \ must be used to quote the characters \ , $, `, and the first character of word. If - is appended to <<, then all leading tabs are stripped from word and from the document.

<&digit

The standard input is duplicated from file descriptor digit (see dup(2)). Similarly for the standard output using >&digit.

<&-

The standard input is closed. Similarly for the standard output using >&-.

<&p

The input from the co-process is moved to standard input.

>&p

The output to the co-process is moved to standard output.

If one of the above is preceded by a digit, then the
file descriptor number referred to is that specified by the digit (instead
of the default 0 or 1). For example:

... 2>&1

means file descriptor 2 is to be opened for writing as a
duplicate of file descriptor 1.

The order in which redirections are specified is significant. The shell evaluates
each redirection in terms of the (file descriptor, file) association at the time
of evaluation. For example:

... 1>fname 2>&1

first associates file descriptor 1 with file fname. It then associates file
descriptor 2 with the file associated with file descriptor 1 (that is,
fname). If the order of redirections were reversed, file descriptor 2 would
be associated with the terminal (assuming file descriptor 1 had been) and then
file descriptor 1 would be associated with file fname.

If a command is followed by & and job control is not
active, then the default standard input for the command is the empty
file /dev/null. Otherwise, the environment for the execution of a command contains
the file descriptors of the invoking shell as modified by input/output specifications.

Environment

The environment (see environ(5)) is a list of name-value pairs that is
passed to an executed program in the same way as a normal argument
list. The names must be identifiers and the values are character strings.
The shell interacts with the environment in several ways. On invocation, the
shell scans the environment and creates a variable for each name found,
giving it the corresponding value and marking it export. Executed commands inherit the
environment. If the user modifies the values of these variables or creates
new ones, using the export or typeset-x commands, they become part
of the environment. The environment seen by any executed command is thus composed
of any name-value pairs originally inherited by the shell, whose values can
be modified by the current shell, plus any additions which must be
noted in export or typeset-x commands.

The environment for any simple-command or function can be augmented by prefixing
it with one or more variable assignments. A variable assignment argument is
a word of the form identifier=value. Thus:

TERM=450 cmd args

and

(export TERM; TERM=450; cmd args)

are equivalent (as far as the above execution of cmd is concerned,
except for special commands listed that are preceded with an asterisk).

If the -k flag is set, all variable assignment arguments are placed
in the environment, even if they occur after the command name. The
following first prints a=b c and then c:

echo a=b c
set -k echo
a=b c

This feature is intended for use with scripts written for early versions
of the shell and its use in new scripts is strongly discouraged.
It is likely to disappear someday.

Functions

The function reserved word, described in the Commands section above, is used
to define shell functions. Shell functions are read in and stored internally.
Alias names are resolved when the function is read. Functions are executed
like commands with the arguments passed as positional parameters. See Execution.

Functions execute in the same process as the caller and share all
files and present working directory with the caller. Traps caught by the
caller are reset to their default action inside the function. A trap
condition that is not caught or ignored by the function causes the
function to terminate and the condition to be passed on to the caller.

A trap on EXIT set inside a function is executed after the
function completes in the environment of the caller. This is true only
for non-POSIX-style functions, that is, functions declared as

function func

as opposed to POSIX-style functions, declared as

func()

Ordinarily, variables are shared between the calling program and the function. However,
the typeset special command used within a function defines local variables whose
scope includes the current function and all functions it calls.

The special command return is used to return from function calls. Errors
within functions return control to the caller.

The names of all functions can be listed with typeset-f. typeset-f
lists all function names as well as the text of all functions.
typeset-ffunction-names lists the text of the named functions only. Functions can
be undefined with the -f option of the unset special command.

Ordinarily, functions are unset when the shell executes a shell script. The
-xf option of the typeset command allows a function to be exported
to scripts that are executed without a separate invocation of the shell.
Functions that need to be defined across separate invocations of the shell should
be specified in the ENV file with the -xf option of typeset.

Function Definition Command

A function is a user-defined name that is used as a simple
command to call a compound command with new positional parameters. A function
is defined with a function definition command.

The format of a function definition command is as follows:

fname()compound-command[io-redirect ...]

The function is named fname; it must be a name. An implementation
can allow other characters in a function name as an extension. The
implementation maintains separate name spaces for functions and variables.

The () in the function definition command consists of two operators. Therefore,
intermixing blank characters with the fname, (, and ) is allowed, but
unnecessary.

The argument compound-command represents a compound command.

When the function is declared, none of the expansions in wordexp is
performed on the text in compound-command or io-redirect; all expansions is performed
as normal each time the function is called. Similarly, the optional io-redirect
redirections and any variable assignments within compound-command is performed during the execution
of the function itself, not the function definition.

When a function is executed, it has the syntax-error and variable-assignment properties
described for the special built-in utilities.

The compound-command is executed whenever the function name is specified as the
name of a simple command The operands to the command temporarily becomes
the positional parameters during the execution of the compound-command; the special parameter #
is also changed to reflect the number of operands. The special parameter
0 is unchanged. When the function completes, the values of the positional
parameters and the special parameter # is restored to the values they
had before the function was executed. If the special built-in return is executed
in the compound-command, the function completes and execution resumes with the next
command after the function call.

An example of how a function definition can be used wherever a
simple command is allowed:

The exit status of a function definition is 0 if the function
was declared successfully; otherwise, it is greater than zero. The exit status
of a function invocation is the exit status of the last command
executed by the function.

Jobs

If the monitor option of the set command is turned on, an
interactive shell associates a job with each pipeline. It keeps a
table of current jobs, printed by the jobs command, and assigns them
small integer numbers. When a job is started asynchronously with &, the shell
prints a line which looks like:

[1] 1234

indicating that the job, which was started asynchronously, was job number 1
and had one (top-level) process, whose process id was 1234.

If you are running a job and wish to do something else
you can press the key ^Z (Control-Z) which sends a STOP signal
to the current job. The shell normally indicates that the job has
been `Stopped', and print another prompt. You can then manipulate the state of
this job, putting it in the background with the bg command, or
run some other commands and then eventually bring the job back into
the foreground with the foreground command fg. A ^Z takes effect immediately and
is like an interrupt in that pending output and unread input are
discarded when it is typed.

A job being run in the background stops if it tries to
read from the terminal. Background jobs are normally allowed to produce output,
but this can be disabled by giving the command “stty tostop”. If you
set this tty option, then background jobs stop when they try to produce
output as they do when they try to read input.

There are several ways to refer to jobs in the shell. A
job can be referred to by the process id of any process
of the job or by one of the following:

%number

The job with the given number.

%string

Any job whose command line begins with string.

%?string

Any job whose command line contains string.

%%

Current job.

%+

Equivalent to %%.

%-

Previous job.

The shell learns immediately whenever a process changes state. It normally informs
you whenever a job becomes blocked so that no further progress is
possible, but only just before it prints a prompt. This is done
so that it does not otherwise disturb your work.

When the monitor mode is on, each background job that completes triggers
any trap set for CHLD.

When you try to leave the shell while jobs are running or
stopped, you are warned with the message, `You have stopped(running) jobs.' You can use the
jobs command to see what they are. If you do this or
immediately try to exit again, the shell does not warn you a second
time, and the stopped jobs is terminated. If you have jobs running
for which the nohup command was invoked and attempt to logout, you
are warned with the message:

You have jobs running.

You need to logout a second time to actually logout. However, your
background jobs continue to run.

Signals

The INT and QUIT signals for an invoked command are ignored if
the command is followed by & and the monitor option is not
active. Otherwise, signals have the values inherited by the shell from its parent.
See the trap special command section.

Execution

Each time a command is executed, the above substitutions are carried out.
If the command name matches one of the Special Commands listed, it is
executed within the current shell process. Next, the command name is checked
to see if it matches one of the user defined functions. If it
does, the positional parameters are saved and then reset to the arguments
of the function call. When the function completes or issues a return,
the positional parameter list is restored and any trap set on EXIT
within the function is executed. The value of a function is the value
of the last command executed. A function is also executed in the
current shell process. If a command name is not a special command or
a user defined function, a process is created and an attempt is made
to execute the command using exec(2).

The shell variable PATH defines the search path for the directory containing
the command. Alternative directory names are separated by a colon (:). The
default path is /bin:/usr/bin: (specifying /bin, /usr/bin, and the current directory in that
order). The current directory can be specified by two or more adjacent
colons, or by a colon at the beginning or end of the
path list. If the command name contains a / then the search
path is not used. Otherwise, each directory in the path is searched for
an executable file. If the file has execute permission but is not
a directory or an a.out file, it is assumed to be a
file containing shell commands. A sub-shell is spawned to read it. All
non-exported aliases, functions, and variables are removed in this case. A parenthesized command
is executed in a sub-shell without removing non-exported quantities.

Command Re-entry

The text of the last HISTSIZE (default 128) commands entered from a
terminal device is saved in a history file. The file $HOME/.sh_history is
used if the HISTFILE variable is not set or if the file
it names is not writable. A shell can access the commands of all
interactive shells which use the same named HISTFILE. The special command fc
is used to list or edit a portion of this file. The
portion of the file to be edited or listed can be selected by
number or by giving the first character or characters of the command.
A single command or range of commands can be specified. If you
do not specify an editor program as an argument to fc then
the value of the variable FCEDIT is used. If FCEDIT is not defined,
then /bin/ed is used. The edited command(s) is printed and re-executed upon
leaving the editor. The editor name - is used to skip the
editing phase and to re-execute the command. In this case a substitution
parameter of the form old=new can be used to modify the command
before execution. For example, if r is aliased to 'fc-e-' then typing 'r bad=good c' re-executes the most recent command which starts with
the letter c, replacing the first occurrence of the string bad with
the string good.

In-line Editing Option

Normally, each command line entered from a terminal device is simply typed
followed by a new-line (RETURN or LINEFEED). If either the emacs, gmacs,
or vi option is active, the user can edit the command line.
To be in either of these edit modes set the corresponding option. An
editing option is automatically selected each time the VISUAL or EDITOR variable
is assigned a value ending in either of these option names.

The editing features require that the user's terminal accept RETURN as carriage
return without line feed and that a space must overwrite the current
character on the screen.

The editing modes implement a concept where the user is looking through
a window at the current line. The window width is the value
of COLUMNS if it is defined, otherwise 80. If the window width
is too small to display the prompt and leave at least 8
columns to enter input, the prompt is truncated from the left. If the
line is longer than the window width minus two, a mark is
displayed at the end of the window to notify the user. As
the cursor moves and reaches the window boundaries the window are centered
about the cursor. The mark is a > if the line extends on
the right side of the window, < if the line extends on
the left, and * if the line extends on both sides of
the window.

The search commands in each edit mode provide access to the history
file. Only strings are matched, not patterns, although a leading caret (^)
in the string restricts the match to begin at the first character
in the line.

emacs Editing Mode

This mode is entered by enabling either the emacs or gmacs option.
The only difference between these two modes is the way they handle
^T. To edit, move the cursor to the point needing correction and
then insert or delete characters or words as needed. All the editing commands
are control characters or escape sequences. The notation for control characters is
caret ( ^ ) followed by the character. For example, ^F is
the notation for control F. This is entered by depressing `f' while holding
down the CTRL (control) key. The SHIFT key is not depressed. (The
notation ^? indicates the DEL (delete) key.)

The notation for escape sequences is M- followed by a character. For
example, M-f (pronounced Meta f) is entered by depressing ESC (ascii 033)
followed by `f'. (M-F would be the notation for ESC followed by
SHIFT (capital) `F'.)

All edit commands operate from any place on the line (not just
at the beginning). Neither the RETURN nor the LINEFEED key is entered
after edit commands except when noted.

^F

Move cursor forward (right) one character.

M-f

Move cursor forward one word. (The emacs editor's idea of a word is a string of characters consisting of only letters, digits and underscores.)

^B

Move cursor backward (left) one character.

M-b

Move cursor backward one word.

^A

Move cursor to start of line.

^E

Move cursor to end of line.

^]char

Move cursor forward to character char on current line.

M-^]char

Move cursor backward to character char on current line.

^X^X

Interchange the cursor and mark.

erase

(User defined erase character as defined by the stty(1) command, usually ^H or #.) Delete previous character.

^D

Delete current character.

M-d

Delete current word.

M-^H

(Meta-backspace) Delete previous word.

M-h

Delete previous word.

M-^?

(Meta-DEL) Delete previous word (if your interrupt character is ^? (DEL, the default) then this command does not work).

^T

Transpose current character with next character in emacs mode. Transpose two previous characters in gmacs mode.

^C

Capitalize current character.

M-c

Capitalize current word.

M-l

Change the current word to lower case.

^K

Delete from the cursor to the end of the line. If preceded by a numerical parameter whose value is less than the current cursor position, then delete from given position up to the cursor. If preceded by a numerical parameter whose value is greater than the current cursor position, then delete from cursor up to given cursor position.

^W

Kill from the cursor to the mark.

M-p

Push the region from the cursor to the mark on the stack.

kill

(User defined kill character as defined by the stty(1) command, usually ^G or @.) Kill the entire current line. If two kill characters are entered in succession, all kill characters from then on cause a line feed (useful when using paper terminals).

^Y

Restore last item removed from line. (Yank item back to the line.)

^L

Line feed and print current line.

^@

(null character) Set mark.

M-space

(Meta space) Set mark.

J

(New line) Execute the current line.

M

(Return) Execute the current line.

eof

End-of-file character, normally ^D, is processed as an End-of-file only if the current line is null.

^P

Fetch previous command. Each time ^P is entered the previous command back in time is accessed. Moves back one line when not on the first line of a multi-line command.

M-<

Fetch the least recent (oldest) history line.

M->

Fetch the most recent (youngest) history line.

^N

Fetch next command line. Each time ^N is entered the next command line forward in time is accessed.

^Rstring

Reverse search history for a previous command line containing string. If a parameter of zero is given, the search is forward. string is terminated by a RETURN or NEW LINE. If string is preceded by a ^, the matched line must begin with string. If string is omitted, then the next command line containing the most recent string is accessed. In this case a parameter of zero reverses the direction of the search.

^O

Operate. Execute the current line and fetch the next line relative to current line from the history file.

M-digits

(Escape) Define numeric parameter, the digits are taken as a parameter to the next command. The commands that accept a parameter are ^F, ^B, erase, ^C, ^D, ^K, ^R, ^P, ^N, ^], M-., M-^], M-_, M-b, M-c, M-d, M-f, M-h, M-l and M-^H.

M-letter

Soft-key. Your alias list is searched for an alias by the name _letter and if an alias of this name is defined, its value is inserted on the input queue. The letter must not be one of the above meta-functions.

M-[letter

Soft-key. Your alias list is searched for an alias by the name __letter and if an alias of this name is defined, its value is inserted on the input queue. The can be used to program functions keys on many terminals.

M-.

The last word of the previous command is inserted on the line. If preceded by a numeric parameter, the value of this parameter determines which word to insert rather than the last word.

M-_

Same as M-..

M-*

An asterisk is appended to the end of the word and a file name expansion is attempted.

M-ESC

File name completion. Replaces the current word with the longest common prefix of all filenames matching the current word with an asterisk appended. If the match is unique, a / is appended if the file is a directory and a space is appended if the file is not a directory.

M-=

List files matching current word pattern if an asterisk were appended.

^U

Multiply parameter of next command by 4.

\

Escape next character. Editing characters, the user's erase, kill and interrupt (normally ^?) characters can be entered in a command line or in a search string if preceded by a \ . The \ removes the next character's editing features (if any).

^V

Display version of the shell.

M-#

Insert a # at the beginning of the line and execute it. This causes a comment to be inserted in the history file.

vi Editing Mode

There are two typing modes. Initially, when you enter a command you
are in the input mode. To edit, enter control mode by typing
ESC (033) and move the cursor to the point needing correction and
then insert or delete characters or words as needed. Most control commands accept
an optional repeat count prior to the command.

When in vi mode on most systems, canonical processing is initially enabled
and the command is echoed again if the speed is 1200 baud
or greater and it contains any control characters or less than one
second has elapsed since the prompt was printed. The ESC character terminates canonical
processing for the remainder of the command and the user can then
modify the command line. This scheme has the advantages of canonical processing
with the type-ahead echoing of raw mode.

If the option viraw is also set, the terminal always have canonical
processing disabled. This mode is implicit for systems that do not support
two alternate end of line delimiters, and can be helpful for certain
terminals.

Input Edit Commands

By default the editor is in input mode.

erase

(User defined erase character as defined by the stty(1) command, usually ^H or #.) Delete previous character.

^W

Delete the previous blank separated word.

^D

Terminate the shell.

^V

Escape next character. Editing characters and the user's erase or kill characters can be entered in a command line or in a search string if preceded by a ^V. The ^V removes the next character's editing features (if any).

\

Escape the next erase or kill character.

Motion Edit Commands

The following commands move the cursor:

[count]l

Cursor forward (right) one character.

[count]w

Cursor forward one alpha-numeric word.

[count]W

Cursor to the beginning of the next word that follows a blank.

[count]e

Cursor to end of word.

[count]E

Cursor to end of the current blank delimited word.

[count]h

Cursor backward (left) one character.

[count]b

Cursor backward one word.

[count]B

Cursor to preceding blank separated word.

[count]|

Cursor to column count.

[count]fc

Find the next character c in the current line.

[count]Fc

Find the previous character c in the current line.

[count]tc

Equivalent to f followed by h.

[count]Tc

Equivalent to F followed by l.

[count];

Repeats count times, the last single character find command, f, F, t, or T.

[count],

Reverses the last single character find command count times.

0

Cursor to start of line.

^

Cursor to first non-blank character in line.

$

Cursor to end of line.

%

Moves to balancing (, ), {, }, [, or ]. If cursor is not on one of the above characters, the remainder of the line is searched for the first occurrence of one of the above characters first.

Search Edit Commands

These commands access your command history.

[count]k

Fetch previous command. Each time k is entered the previous command back in time is accessed.

[count]-

Equivalent to k.

[count]j

Fetch next command. Each time j is entered, the next command forward in time is accessed.

[count]+

Equivalent to j.

[count]G

The command number count is fetched. The default is the least recent history command.

/string

Search backward through history for a previous command containing string. string is terminated by a RETURN or NEWLINE. If string is preceded by a ^, the matched line must begin with string. If string is NULL, the previous string is used.

?string

Same as / except that search is in the forward direction.

n

Search for next match of the last pattern to / or ? commands.

N

Search for next match of the last pattern to / or ?, but in reverse direction. Search history for the string entered by the previous / command.

Text Modification Edit Commands

These commands modifies the line.

a

Enter input mode and enter text after the current character.

A

Append text to the end of the line. Equivalent to $a.

[count]cmotion

c[count]motion

Delete current character through the character that motion would move the cursor to and enter input mode. If motion is c, the entire line is deleted and input mode entered.

C

Delete the current character through the end of line and enter input mode. Equivalent to c$.

[count]s

Delete count characters and enter input mode.

S

Equivalent to cc.

D

Delete the current character through the end of line. Equivalent to d$.

[count]dmotion

d[count]motion

Delete current character through the character that motion would move to. If motion is d, the entire line is deleted.

i

Enter input mode and insert text before the current character.

I

Insert text before the beginning of the line. Equivalent to 0i.

[count]P

Place the previous text modification before the cursor.

[count]p

Place the previous text modification after the cursor.

R

Enter input mode and replace characters on the screen with characters you type overlay fashion.

[count]rc

Replace the count character(s) starting at the current cursor position with c, and advance the cursor.

[count]x

Delete current character.

[count]X

Delete preceding character.

[count].

Repeat the previous text modification command.

[count]~

Invert the case of the count character(s) starting at the current cursor position and advance the cursor.

[count]_

Causes the count word of the previous command to be appended and input mode entered. The last word is used if count is omitted.

*

Causes an * to be appended to the current word and file name generation attempted. If no match is found, it rings the bell. Otherwise, the word is replaced by the matching pattern and input mode is entered.

\

Filename completion. Replaces the current word with the longest common prefix of all filenames matching the current word with an asterisk appended. If the match is unique, a / is appended if the file is a directory and a space is appended if the file is not a directory.

Other Edit Commands

Miscellaneous commands.

[count]ymotion

y[count]motion

Yank current character through character that motion would move the cursor to and puts them into the delete buffer. The text and cursor are unchanged.

Y

Yanks from current position to end of line. Equivalent to y$.

u

Undo the last text modifying command.

U

Undo all the text modifying commands performed on the line.

[count]v

Returns the command fc-e${VISUAL:-${EDITOR:–vi}}count in the input buffer. If count is omitted, then the current line is used.

^L

Line feed and print current line. Has effect only in control mode.

J

(New line) Execute the current line, regardless of mode.

M

(Return) Execute the current line, regardless of mode.

#

If the first character of the command is a #, then this command deletes this # and each # that follows a newline. Otherwise, sends the line after inserting a # in front of each line in the command. Useful for causing the current line to be inserted in the history as a comment and removing comments from previous comment commands in the history file.

=

List the file names that match the current word if an asterisk were appended it.

@letter

Your alias list is searched for an alias by the name _letter and if an alias of this name is defined, its value is inserted on the input queue for processing.

Special Commands

The following simple-commands are executed in the shell process. Input/Output redirection is
permitted. Unless otherwise indicated, the output is written on file descriptor 1
and the exit status, when there is no syntax error, is 0.
Commands that are preceded by one or two * (asterisks) are treated specially
in the following ways:

Variable assignment lists preceding the command remain in effect when the command completes.

I/O redirections are processed after variable assignments.

Errors cause a script that contains them to abort.

Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.

* : [ arg ... ]

The command only expands parameters.

* .file [ arg ... ]

Read the complete file then execute the commands. The commands are executed in the current shell environment. The search path specified by PATH is used to find the directory containing file. If any arguments arg are given, they become the positional parameters. Otherwise the positional parameters are unchanged. The exit status is the exit status of the last command executed.

** alias [ -tx ] [ name[ =value ] ] ...

alias with no arguments prints the list of aliases in the form name=value on standard output. An alias is defined for each name whose value is given. A trailing space in value causes the next word to be checked for alias substitution. The -t flag is used to set and list tracked aliases. The value of a tracked alias is the full pathname corresponding to the given name. The value becomes undefined when the value of PATH is reset but the aliases remained tracked. Without the -t flag, for each name in the argument list for which no value is given, the name and value of the alias is printed. The -x flag is used to set or print exported aliases. An exported alias is defined for scripts invoked by name. The exit status is non-zero if a name is given, but no value, and no alias has been defined for the name.

bg [ %job... ]

This command is only on systems that support job control. Puts each specified job into the background. The current job is put in the background if job is not specified. See Jobs section above for a description of the format of job.

* break [ n ]

Exit from the enclosed for, while, until, or select loop, if any. If n is specified then breakn levels. If n is greater than the number of enclosing loops, the outermost enclosing loop shall be exited.

* continue [ n ]

Resume the next iteration of the enclosed for, while, until, or select loop. If n is specified then resume at the n-th enclosed loop. If n is greater than the number of enclosing loops, the outermost enclosing loop shall be used.

cd [ -L ] [ -P ] [ arg ]

cdold new

This command can be in either of two forms. In the first form it changes the current directory to arg. If arg is - the directory is changed to the previous directory. The shell variable HOME is the default arg. The environment variable PWD is set to the current directory. If the PWD is changed, the OLDPWD environment variable shall also be changed to the value of the old working directory, that is, the current working directory immediately prior to the call to change directory (cd). The shell variable CDPATH defines the search path for the directory containing arg. Alternative directory names are separated by a colon (:). The default path is null (specifying the current directory). The current directory is specified by a null path name, which can appear immediately after the equal sign or between the colon delimiters anywhere else in the path list. If arg begins with a / then the search path is not used. Otherwise, each directory in the path is searched for arg. If unsuccessful, cd attempts to change directories to the pathname formed by the concatenation of the value of PWD, a slash character, and arg.

If both -L and -P options are specified, the last option to be invoked is used and the other is ignored. If neither -L nor -P is specified, the operand is handled dot-dot logically.

The second form of cd substitutes the string new for the string old in the current directory name, PWD, and tries to change to this new directory. The cd command cannot be executed by rksh.

command [-p] [command_name] [argument ...]

command [-v|-V] command_name

The command utility causes the shell to treat the arguments as a simple command, suppressing the shell function lookup. The -p flag performs the command search using a default value for PATH that is guaranteed to find all of the standard utilities. The -v flag writes a string to standard output that indicates the pathname or command that is used by the shell, in the current shell execution environment, to invoke command_name. The -V flag writes a string to standard output that indicates how the name given in the command_name operand is interpreted by the shell, in the current shell execution environment.

The arguments are read as input to the shell and the resulting command(s) executed.

* exec [ arg ... ]

If arg is given, the command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments can appear and affect the current process. If no arguments are given the effect of this command is to modify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are opened with this mechanism are closed when invoking another program.

* exit [ n ]

Causes the calling shell or shell script to exit with the exit status specified by n. The value is the least significant 8 bits of the specified status. If n is omitted then the exit status is that of the last command executed. When exit occurs when executing a trap, the last command refers to the command that executed before the trap was invoked. An EOF also causes the shell to exit except for a shell which has the ignoreeof option turned on. See set.

** export [ name[=value] ] ...

** export-p

The given names are marked for automatic export to the environment of subsequently-executed commands.

When -p is specified, export writes to the standard output the names and values of all exported variables in the following format:

"export %s=%s\n", name, value

if name is set, and:

"export %s\n", name

if name is unset.

The shell formats the output, including the proper use of quoting, so that it is suitable for reinput to the shell as commands that achieve the same exporting results, except for the following:

Read-only variables with values cannot be reset.

Variables that were unset at the time they were output are not reset to the unset state if a value is assigned to the variable between the time the state was saved and the time at which the saved output is reinput to the shell.

fc [ -eename ] [ -nlr ] [ first [ last ] ]

fc-e- [ old=new ] [ command ]

fc-s [ old=new ] [ command ]

In the first form, a range of commands from first to last is selected from the last HISTSIZE commands that were typed at the terminal. The arguments first and last can be specified as a number or as a string. A string is used to locate the most recent command starting with the given string. A negative number is used as an offset to the current command number. If the -l flag is selected, the commands are listed on standard output. Otherwise, the editor program ename is invoked on a file containing these keyboard commands. If ename is not supplied, then the value of the variable FCEDIT (default /bin/ed) is used as the editor. When editing is complete, the edited command(s) is executed. If last is not specified then it is set to first. If first is not specified the default is the previous command for editing and -16 for listing. The flag -r reverses the order of the commands and the flag -n suppresses command numbers when listing. In the second form the command is re-executed after the substitution old=new is performed. If there is not a command argument, the most recent command typed at this terminal is executed.

fg [ %job... ]

This command is only on systems that support job control. Each job specified is brought to the foreground. Otherwise, the current job is brought into the foreground. See “Jobs” section above for a description of the format of job.

getoptsoptstring name [ arg ... ]

Checks arg for legal options. If arg is omitted, the positional parameters are used. An option argument begins with a + or a -. An option not beginning with + or - or the argument – ends the options. optstring contains the letters that getopts recognizes. If a letter is followed by a :, that option is expected to have an argument. The options can be separated from the argument by blanks.

getopts places the next option letter it finds inside variable name each time it is invoked with a + prepended when arg begins with a +. The index of the next arg is stored in OPTIND. The option argument, if any, gets stored in OPTARG.

A leading : in optstring causes getopts to store the letter of an invalid option in OPTARG, and to set name to ? for an unknown option and to : when a required option is missing. Otherwise, getopts prints an error message. The exit status is non-zero when there are no more options. See getoptcvt(1) for usage and description.

getopts supports both traditional single-character short options and long options defined by Sun's Command Line Interface Paradigm (CLIP).

Each long option is an alias for a short option and is specified in parentheses following its equivalent short option. For example, you can specify the long option file as an alias for the short option f using the following script line:

getopts "f(file)" opt

Precede long options on the command line with -- or ++. In the example above, --file on the command line would be the equivalent of -f, and ++file on the command line would be the equivalent of +f.

Each short option can have multiple long option equivalents, although this is in violation of the CLIP specification and should be used with caution. You must enclose each long option equivalent parentheses, as follows:

getopts "f:(file)(input-file)o:(output-file)"

In the above example, both --file and --input-file are the equivalent of -f, and --output-file is the equivalent of -o.

The variable name is always set to a short option. When a long option is specified on the command line, name is set to the short-option equivalent.

hash [ name ... ]

hash [ -r ]

For each name, the location in the search path of the command specified by name is determined and remembered by the shell. The -r option causes the shell to forget all remembered locations. If no arguments are given, information about remembered commands is presented. Hits is the number of times a command has been invoked by the shell process. Cost is a measure of the work required to locate a command in the search path. If a command is found in a relative directory in the search path, after changing to that directory, the stored location of that command is recalculated. Commands for which this is done are indicated by an asterisk (*) adjacent to the hits information. Cost is incremented when the recalculation is done.

jobs [ -lnp ] [ %job ... ]

Lists information about each given job; or all active jobs if job is omitted. The -l flag lists process ids in addition to the normal information. The -n flag displays only jobs that have stopped or exited since last notified. The -p flag causes only the process group to be listed. See Jobs section above and jobs(1) for a description of the format of job.

kill [ -sig ] %job ...

kill [ -sig ] pid ...

kill-l

Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by number or by names (as given in signal.h(3HEAD) stripped of the prefix ``SIG'' with the exception that SIGCHD is named CHLD). If the signal being sent is TERM (terminate) or HUP (hangup), then the job or process is sent a CONT (continue) signal if it is stopped. The argument job can be the process id of a process that is not a member of one of the active jobs. See Jobs for a description of the format of job. In the second form, kill-l, the signal numbers and names are listed.

letarg...

Each arg is a separate arithmetic expression to be evaluated. See the Arithmetic Evaluation section above, for a description of arithmetic expression evaluation.

The exit status is 0 if the value of the last expression is non-zero, and 1 otherwise.

loginargument . . .

Equivalent to `exec login argument....' See login(1) for usage and description.

* newgrp [ arg ... ]

Equivalent to exec /bin/newgrparg ....

print [ -Rnprsu[n ] ] [ arg ... ]

The shell output mechanism. With no flags or with flag - or –, the arguments are printed on standard output as described by echo(1). The exit status is 0, unless the output file is not open for writing.

-n

Suppresses NEWLINE from being added to the output.

-R | -r

Raw mode. Ignores the escape conventions of echo. The -R option prints all subsequent arguments and options other than -n.

-p

Writes the arguments to the pipe of the process spawned with |& instead of standard output.

-s

Writes the arguments to the history file instead of standard output.

-u [ n ]

Specifies a one digit file descriptor unit number n on which the output is placed. The default is 1.

pwd [ -L | -P ]

Writes to the standard output an absolute pathname of the current working directory, which does not contain the filenames dot (.) or dot-dot (..).

-L

If the PWD environment variable contains an absolute pathname of the current directory that does not contain the filenames dot or dot-dot, pwd writes this pathname to standard output. Otherwise, the -L option behaves like the -P option.

-P

The absolute pathname written shall not contain filenames that, in the context of the pathname, refer to files of type symbolic link.

If both -L and -P are specified, the last one applies. If neither -L nor -P is specified, pwd behaves as if -L had been specified.

read [ -prsu[ n ] ] [ name?prompt ] [ name ... ]

The shell input mechanism. One line is read and is broken up into fields using the characters in IFS as separators. The escape character, (\), is used to remove any special meaning for the next character and for line continuation. In raw mode, -r, the \ character is not treated specially. The first field is assigned to the first name, the second field to the second name, etc., with leftover fields assigned to the last name. The -p option causes the input line to be taken from the input pipe of a process spawned by the shell using |&. If the -s flag is present, the input is saved as a command in the history file. The flag -u can be used to specify a one digit file descriptor unit n to read from. The file descriptor can be opened with the exec special command. The default value of n is 0. If name is omitted then REPLY is used as the default name. The exit status is 0 unless the input file is not open for reading or an EOF is encountered. An EOF with the -p option causes cleanup for this process so that another can be spawned. If the first argument contains a ?, the remainder of this word is used as a prompt on standard error when the shell is interactive. The exit status is 0 unless an EOF is encountered.

** readonly [ name[=value] ] ...

** readonly-p

The given names are marked readonly and these names cannot be changed by subsequent assignment.

When -p is specified, readonly writes to the standard output the names and values of all read-only variables, in the following format:

"readonly %s=%s\n", name, value

if name is set, and:

"readonly $s\n", name

if name is unset.

The shell formats the output, including the proper use of quoting, so that it is suitable for reinput to the shell as commands that achieve the same value and readonly attribute-setting results in a shell execution environment in which:

Variables with values set at the time they were output do not have the readonly attribute set.

Variables that were unset at the time they were output do not have a value at the time at which the saved output is reinput to the shell.

* return [ n ]

Causes a shell function or '.' script to return to the invoking script with the return status specified by n. The value is the least significant 8 bits of the specified status. If n is omitted then the return status is that of the last command executed. If return is invoked while not in a function or a '.' script, then it is the same as an exit.

set [ ±abCefhkmnopstuvx ] [ ±ooption ]. . . [ ±Aname ] [ arg ... ]

The flags for this command have meaning as follows:

-A

Array assignment. Unsets the variable name and assigns values sequentially from the list arg. If +A is used, the variable name is not unset first.

-a

All subsequent variables that are defined are automatically exported.

-b

Causes the shell to notify the user asynchronously of background job completions. The following message is written to standard error:

"[%d]%c %s%s\n", <job-number>, <current>, <status>, \
<job-name>

where the fields are as follows:

<current>

The character + identifies the job that would be used as a default for the fg or bg utilities. This job can also be specified using the job_id%+ or %%. The character - identifies the job that would become the default if the current default job were to exit; this job can also be specified using the job_id%-. For other jobs, this field is a space character. At most one job can be identified with + and at most one job can be identified with -. If there is any suspended job, then the current job is a suspended job. If there are at least two suspended jobs, then the previous job is also a suspended job.

<job-number>

A number that can be used to identify the process group to the wait, fg, bg, and kill utilities. Using these utilities, the job can be identified by prefixing the job number with %.

<status>

Unspecified.

<job-name>

Unspecified.

When the shell notifies the user a job has been completed, it can remove the job's process ID from the list of those known in the current shell execution environment. Asynchronous notification is not enabled by default.

-C

Prevents existing files from being overwritten by the shell's > redirection operator. The >| redirection operator overrides this noclobber option for an individual file.

-e

If a command has a non-zero exit status, executes the ERR trap, if set, and exit. This mode is disabled while reading profiles.

-f

Disables file name generation.

-h

Each command becomes a tracked alias when first encountered.

-k

All variable assignment arguments are placed in the environment for a command, not just those that precede the command name.

-m

Background jobs runs in a separate process group and a line prints upon completion. The exit status of background jobs is reported in a completion message. On systems with job control, this flag is turned on automatically for interactive shells.

-n

Reads commands and check them for syntax errors, but do not execute them. Ignored for interactive shells.

-o

Writes the current option settings to standard output in a format that is suitable for reinput to the shell as commands that achieve the same option settings.

-o

The following argument can be one of the following option names:

allexport

Same as -a.

errexit

Same as -e.

bgnice

All background jobs are run at a lower priority. This is the default mode.

emacs

Puts you in an emacs style in-line editor for command entry.

gmacs

Puts you in a gmacs style in-line editor for command entry.

ignoreeof

The shell does not exit onEOF. The command exit must be used.

keyword

Same as -k.

markdirs

All directory names resulting from file name generation have a trailing / appended.

Puts you in insert mode of a vi style in-line editor until you hit escape character 033. This puts you in control mode. A return sends the line.

viraw

Each character is processed as it is typed in vi mode.

xtrace

Same as -x.

If no option name is supplied, the current option settings are printed.

-p

Disables processing of the $HOME/.profile file and uses the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective uid is not equal to the real uid, or when the effective gid is not equal to the real gid. Turning this off causes the effective uid and gid to be set to the real uid and gid.

-s

Sorts the positional parameters lexicographically.

-t

Exits after reading and executing one command.

-u

Treats unset parameters as an error when substituting.

-v

Prints shell input lines as they are read.

-x

Prints commands and their arguments as they are executed.

-

Turns off -x and -v flags and stops examining arguments for flags.

--

Does not change any of the flags. Useful in setting $1 to a value beginning with -. If no arguments follow this flag then the positional parameters are unset.

Using + rather than - causes these flags to be turned off. These flags can also be used upon invocation of the shell. The current set of flags can be found in $-. Unless -A is specified, the remaining arguments are positional parameters and are assigned, in order, to $1$2 .... If no arguments are given, the names and values of all variables are printed on the standard output.

* shift [ n ]

The positional parameters from $n+1$n+1 . . . are renamed $1 . . ., default n is 1. The parameter n can be any arithmetic expression that evaluates to a non-negative number less than or equal to $#.

stop%jobid ...

stoppid ...

stop stops the execution of a background job(s) by using its jobid, or of any process by using its pid. See ps(1).

suspend

Stops the execution of the current shell (but not if it is the login shell).

Prints the accumulated user and system times for the shell and for processes run from the shell.

* trap [ argsig ... ]

arg is a command to be read and executed when the shell receives signal(s) sig. arg is scanned once when the trap is set and once when the trap is taken. sig can be specified as a signal number or signal name. trap commands are executed in order of signal number. Any attempt to set a trap on a signal number that was ignored on entry to the current shell is ineffective.

If arg is -, the shell resets each sig to the default value. If arg is null (''), the shell ignores each specified sig if it arises. Otherwise, arg is read and executed by the shell when one of the corresponding sigs arises. The action of the trap overrides a previous action (either default action or one explicitly set). The value of $? after the trap action completes is the value it had before the trap was invoked.

sig can be EXIT,0 (equivalent to EXIT) or a signal specified using a symbolic name, without the SIG prefix, for example, HUP, INT, QUIT, TERM. If sig is 0 or EXIT and the trap statement is executed inside the body of a function, then the command arg is executed after the function completes. If sig is 0 or EXIT for a trap set outside any function, the command arg is executed on exit from the shell. If sig is ERR, arg is executed whenever a command has a non-zero exit status. If sig is DEBUG, arg is executed after each command.

The environment in which the shell executes a trap on EXIT is identical to the environment immediately after the last command executed before the trap on EXIT was taken.

Each time the trap is invoked, arg is processed in a manner equivalent to eval "$arg".

Signals that were ignored on entry to a non-interactive shell cannot be trapped or reset, although no error need be reported when attempting to do so. An interactive shell can reset or catch signals ignored on entry. Traps remain in place for a given shell until explicitly changed with another trap command.

When a subshell is entered, traps are set to the default args. This does not imply that the trap command cannot be used within the subshell to set new traps.

The trap command with no arguments writes to standard output a list of commands associated with each sig. The format is:

trap -- %s %s ... <arg>, <sig> ...

The shell formats the output, including the proper use of quoting, so that it is suitable for reinput to the shell as commands that achieve the same trapping results. For example:

save_traps=$(trap) . . . eval "$save_traps"

If the trap name or number is invalid, a non-zero exit status is returned. Otherwise, 0 is returned. For both interactive and non-interactive shells, invalid signal names or numbers are not considered a syntax error and dol not cause the shell to abort.

Traps are not processed while a job is waiting for a foreground process. Thus, a trap on CHLD won't be executed until the foreground job terminates.

typename ...

For each name, indicates how it would be interpreted if used as a command name.

** typeset [ ±HLRZfilrtux[n] ] [ name[=value ] ] ...

Sets attributes and values for shell variables and functions. When typeset is invoked inside a function, a new instance of the variables name is created. The variables value and type are restored when the function completes. The following list of attributes can be specified:

Left justifies and removes leading blanks from value. If n is non-zero it defines the width of the field. Otherwise, it is determined by the width of the value of first assignment. When the variable is assigned to, it is filled on the right with blanks or truncated, if necessary, to fit into the field. Leading zeros are removed if the -Z flag is also set. The -R flag is turned off.

-R

Right justifies and fills with leading blanks. If n is non-zero it defines the width of the field, otherwise it is determined by the width of the value of first assignment. The field is left filled with blanks or truncated from the end if the variable is reassigned. The -L flag is turned off.

-Z

Right justifies and fills with leading zeros if the first non-blank character is a digit and the -L flag has not been set. If n is non-zero it defines the width of the field. Otherwise, it is determined by the width of the value of first assignment.

-f

The names refer to function names rather than variable names. No assignments can be made and the only other valid flags are -t, -u, and -x. The flag -t turns on execution tracing for this function. The flag -u causes this function to be marked undefined. The FPATH variable is searched to find the function definition when the function is referenced. The flag -x allows the function definition to remain in effect across shell procedures invoked by name.

-i

Parameter is an integer. This makes arithmetic faster. If n is non-zero it defines the output arithmetic base; otherwise, the first assignment determines the output base.

-l

All upper-case characters are converted to lower-case. The upper-case flag, -u is turned off.

-r

The given names are marked readonly and these names cannot be changed by subsequent assignment.

-t

Tags the variables. Tags are user definable and have no special meaning to the shell.

-u

All lower-case characters are converted to upper-case characters. The lower-case flag, -l is turned off.

-x

The given names are marked for automatic export to the environment of subsequently-executed commands.

The -i attribute cannot be specified along with -R, -L, -Z, or -f.

Using + rather than - causes these flags to be turned off. If no name arguments are given but flags are specified, a list of names (and optionally the values) of the variables which have these flags set is printed. (Using + rather than - keeps the values from being printed.) If no names and flags are given, the names and attributes of all variables are printed.

ulimit [ -HSacdfnstv ] [ limit ]

Sets or displays a resource limit. The available resources limits are listed in the following section. Many systems do not contain one or more of these limits. The limit for a specified resource is set when limit is specified. The value of limit can be a number in the unit specified with each resource, or the value unlimited. The H and S flags specify whether the hard limit or the soft limit for the given resource is set. A hard limit cannot be increased once it is set. A soft limit can be increased up to the value of the hard limit. If neither the H or S options is specified, the limit applies to both. The current resource limit is printed when limit is omitted. In this case, the soft limit is printed unless H is specified. When more than one resource is specified, the limit name and unit is printed before the value.

-a

Lists all of the current resource limits.

-c

The number of 512-byte blocks on the size of core dumps.

-d

The number of K-bytes on the size of the data area.

-f

The number of 512-byte blocks on files written by child processes (files of any size can be read).

-n

The number of file descriptors plus 1.

-s

The number of K-bytes on the size of the stack area.

-t

The number of seconds to be used by each process.

-v

The number of K-bytes for virtual memory.

If no option is given, -f is assumed.

umask [-S] [ mask ]

The user file-creation mask is set to mask (see umask(2)). mask can either be an octal number or a symbolic value as described in chmod(1). If a symbolic value is given, the new umask value is the complement of the result of applying mask to the complement of the previous umask value. If mask is omitted, the current value of the mask is printed. The -S flag produces symbolic output.

unaliasname ...

unalias-a

The aliases given by the list of names are removed from the alias list. The -a option removes all alias definitions from the current execution environment.

unset [ -f ] name ...

The variables given by the list of names are unassigned, that is, their values and attributes are erased. readonly variables cannot be unset. If the -f, flag is set, then the names refer to function names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ removes their special meaning even if they are subsequently assigned to.

* wait [ job ]

Waits for the specified job and report its termination status. If job is not given then all currently active child processes are waited for. The exit status from this command is that of the process waited for. See Jobs for a description of the format of job.

whence [ -pv ] name ...

For each name, indicates how it would be interpreted if used as a command name.

The -v flag produces a more verbose report.

The -p flag does a path search for name even if name is an alias, a function, or a reserved word.

Invocation

If the shell is invoked by exec(2), and the first character of
argument zero ($0) is -, then the shell is assumed to be a
login shell and commands are read from /etc/profile and then from either
.profile in the current directory or $HOME/.profile, if either file exists. Next,
commands are read from the file named by performing parameter substitution on the
value of the environment variable ENV if the file exists. If the
-s flag is not present and arg is, then a path search
is performed on the first arg to determine the name of the
script to execute. The script arg must have read permission and any setuid
and setgid settings are ignored. If the script is not found on
the path, arg is processed as if it named a builtin command
or function. Commands are then read as described as follows. The following flags
are interpreted by the shell when it is invoked:

-c

Reads commands from the command_string operand. Sets the value of special parameter 0 from the value of the command_name operand and the positional parameters ($1, $2, and so on) in sequence from the remaining arg operands. No commands are read from the standard input.

-s

If the -s flag is present or if no arguments remain, commands are read from the standard input. Shell output, except for the output of the Special Commands listed above, is written to file descriptor 2.

-i

If the -i flag is present or if the shell input and output are attached to a terminal (as told by ioctl(2)), then this shell is interactive. In this case, TERM is ignored (so that kill0 does not kill an interactive shell) and INTR is caught and ignored (so that wait is interruptible). In all cases, QUIT is ignored by the shell.

-r

If the -r flag is present the shell is a restricted shell.

The remaining flags and arguments are described under the set command above.

rksh Only

rksh is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell. The actions
of rksh are identical to those of ksh, except that the following
are disallowed:

The restrictions above are enforced after .profile and the ENV files are
interpreted.

When a command to be executed is found to be a shell
procedure, rksh invokes ksh to execute it. Thus, it is possible to
provide to the end-user shell procedures that have access to the full
power of the standard shell, while imposing a limited menu of commands; this
scheme assumes that the end-user does not have write and execute permissions
in the same directory.

The net effect of these rules is that the writer of the
.profile has complete control over user actions, by performing guaranteed setup actions
and leaving the user in an appropriate directory (probably not the login
directory).

The system administrator often sets up a directory of commands (that is,
/usr/rbin) that can be safely invoked by rksh.

Errors

Errors detected by the shell, such as syntax errors, cause the shell
to return a non-zero exit status. Otherwise, the shell returns the exit
status of the last command executed (see also the exit command above).
If the shell is being used non-interactively then execution of the shell file
is abandoned. Run time errors detected by the shell are reported by
printing the command or function name and the error condition. If the
line number that the error occurred on is greater than one, then
the line number is also printed in square brackets ([]) after the command
or function name.

For a non-interactive shell, an error condition encountered by a special built-in
or other type of utility causes the shell to write a diagnostic
message to standard error and exit as shown in the following table:

Error

Special
Built-in

Other Utilities

Shell language syntax error

exits

exits

Utility syntax error (option or operand error)

exits

does not
exit

Redirection error

exits

does not exit

Variable assignment error

exits

does not exit

Expansion error

exits

exits

Command not found

n/a

might exit

Dot
script not found

exits

n/a

An expansion error is one that occurs when the shell expansions are
carried out (for example, ${x!y}, because ! is not a valid operator).
An implementation can treat these as syntax errors if it is able
to detect them during tokenization, rather than during expansion.

If any of the errors shown as “might exit” or “exits” occur
in a subshell, the subshell exits or might exit with a non-zero
status, but the script containing the subshell does not exit because of
the error.

In all of the cases shown in the table, an interactive shell
writes a diagnostic message to standard error without exiting.

Usage

See largefile(5) for the description of the behavior of ksh and rksh
when encountering files greater than or equal to 2 Gbyte (231 bytes).

Exit Status

Each command has an exit status that can influence the behavior of
other shell commands. The exit status of commands that are not utilities
is documented in this section. The exit status of the standard utilities
is documented in their respective sections.

If a command is not found, the exit status is 127. If
the command name is found, but it is not an executable utility,
the exit status is 126. Applications that invoke utilities without using the
shell should use these exit status values to report similar errors.

If a command fails during word expansion or redirection, its exit status
is greater than zero.

When reporting the exit status with the special parameter ?, the shell
reports the full eight bits of exit status available. The exit status
of a command that terminated because it received a signal reported as
greater than 128.

Warnings

The use of setuid shell scripts is strongly discouraged.

Notes

If a command which is a tracked alias is executed, and then a
command with the same name is installed in a directory in the
search path before the directory where the original command was found, the
shell continues to exec the original command. Use the -t option of the
alias command to correct this situation.

Some very old shell scripts contain a ^ as a synonym for
the pipe character |.

Using the fc built-in command within a compound command causes the whole
command to disappear from the history file.

The built-in command .file reads the whole file before any commands are
executed. Therefore, alias and unalias commands in the file does not apply
to any functions defined in the file.

When the shell executes a shell script that attempts to execute a
non-existent command interpreter, the shell returns an erroneous diagnostic message that the
shell script file does not exist.